int NegamaxAlphaBetaSearcher::EvaluateNegaMax(GameState& state, int max_player_id)
{
if(state.GetCurrentPlayer() == max_player_id)
return state.Evaluate(max_player_id);
else
return -state.Evaluate(max_player_id);
}
int NegamaxAlphaBetaSearcher::SearchBestPlay(const GameState& state, int depth)
{
std::vector<int> bestCell;
int bestValue = -INFINITY;
int bestPos = 0;
#ifdef _DEBUG
_searcherCounter = 0;
#endif
ResetTranspositionTable();
GameState tryState = state;
int player_id = state.GetCurrentPlayer();
std::vector<MOVES_LIST> moves;
int mc = tryState.FindMoves(player_id, moves);
if(mc == 0) //遇到无路可走的情况，比如被对方逼着走禁手，可放弃一步
{
return -1;
}
SortMoves(moves);
for(int i = 0; i < mc; i++)
{
tryState.DoPutChess(moves[i].cell, player_id);
int value = NegaMax(tryState, depth - 1, -INFINITY, INFINITY, player_id);
tryState.UndoPutChess(moves[i].cell);
if(value > bestValue)
{
bestValue = value;
bestCell.clear();
bestCell.push_back(moves[i].cell);
}
else if(value == bestValue)
{
bestCell.push_back(moves[i].cell);
}
}
if(bestCell.size() > 0)
bestPos = rand() % bestCell.size();
#ifdef _DEBUG
std::cout << "NegamaxSearcher " << _searcherCounter << " (with Alpha-Beta)" << std::endl;
#endif
return bestCell[bestPos];
}
int NegamaxAlphaBetaSearcher::NegaMax(GameState& state, int depth, int alpha, int beta, int max_player_id)
{
int alphaOrig = alpha;
#if 0
unsigned int state_hash = state.GetHash();
//查询置换表
TT_ENTRY ttEntry = { 0 };
if(LookupTranspositionTable(state_hash, ttEntry) && (ttEntry.depth >= depth))
{
if(ttEntry.flag == TT_FLAG_EXACT)
return ttEntry.value;
else if(ttEntry.flag == TT_FLAG_LOWERBOUND)
alpha = std::max(alpha, ttEntry.value);
else// if(ttEntry.flag == TT_FLAG_UPPERBOUND)
beta = std::min(beta, ttEntry.value);
if(beta <= alpha)
return ttEntry.value;
}
#endif
if(state.IsGameOver() || (depth == 0))
{
#ifdef _DEBUG
_searcherCounter++;
#endif
return EvaluateNegaMax(state, max_player_id);
}
state.SwitchPlayer();
int score = -INFINITY;
int player_id = state.GetCurrentPlayer();
std::vector<MOVES_LIST> moves;
int mc = state.FindMoves(player_id, moves);
SortMoves(moves);
for(int i = 0; i < mc; i++)
{
state.DoPutChess(moves[i].cell, player_id);
int value = -NegaMax(state, depth - 1, -beta, -alpha, max_player_id);
state.UndoPutChess(moves[i].cell);
score = std::max(score, value);
alpha = std::max(alpha, value);
if(beta <= alpha)
break;
}
state.SwitchPlayer();
#if 0
//写入置换表
ttEntry.value = score;
if(score <= alphaOrig)
ttEntry.flag = TT_FLAG_UPPERBOUND;
else if(score >= beta)
ttEntry.flag = TT_FLAG_LOWERBOUND;
else
ttEntry.flag = TT_FLAG_EXACT;
ttEntry.depth = depth;
StoreTranspositionTable(state_hash, ttEntry);
#endif
return score;
}
//Get Best Move -
//recursive min/max algorithm explores game states and
//returns a move and its score, for a specific player
MoveScore GetBestMove( const GameState& theGame, const int player_index, int abPrune, const int recursive=1)
{
const Change& player_change = theGame.GetPlayerChange( theGame.GetCurrentPlayer() );
const Change& pool = theGame.GetGameChange();
int bestScore = (player_index == theGame.GetCurrentPlayer())?
std::numeric_limits<int>::min()
:
std::numeric_limits<int>::max();
Coin bestCoin;
Change bestChange;
Change::List* someChange;
if (recycledChangeLists.empty()){
someChange = new Change::List;
}
else{
someChange = recycledChangeLists.back();
recycledChangeLists.pop_back();
}
//for each coin that can be played
for (const Coin *ci=&COINLIST[0];ci!=&COINLIST[COIN_COUNT];++ci){
if (player_change.GetCount(*ci) > 0){
//get all possible sets of change into array
GetAllPossibleChange(
pool,
*ci,
*someChange);
//for each possible set of change
//(reversed iteration improves AB prune by as much as 70%)
const Change::List::reverse_iterator end = someChange->rend();
for(Change::List::reverse_iterator i = someChange->rbegin();i!=end;++i){
//create "move" from coin to give, and change to take
const Move myMove(*ci,*i);
//create gamestate once the move has been played
GameState newGame = theGame.PlayMove( myMove );
//get "score" for this move
int score;
if (recursive>0 && newGame.GetActivePlayers()>1){
//recursivly examine move, get its score
score = GetBestMove( newGame, player_index, bestScore, recursive-1).score;
}
else{
//leaf node - just get heuristic value
score = GameHeuristic( newGame, player_index, myHeuristic );
}
//Min/Max search
if ((player_index == theGame.GetCurrentPlayer() && score > bestScore) ||
(player_index != theGame.GetCurrentPlayer() && score < bestScore))
{
bestScore = score;
bestCoin = *ci;
bestChange = *i;
//Alpha/Beta pruning
if ((player_index == theGame.GetCurrentPlayer() && score > abPrune) ||
(player_index != theGame.GetCurrentPlayer() && score < abPrune)){
goto exit;
}
}
}
}
}
exit:
recycledChangeLists.push_back( someChange );
return MoveScore( Move( bestCoin, bestChange ), bestScore );
}